Process for production of modified carbon black for rubber reinforcement and process of production of rubber composition containing modified carbon black

ABSTRACT

A process for production of a modified carbon black, at a cheaper cost, for rubber reinforcement having the superior tan δ temperature dependence of silica and an excellent abrasion resistance and further having no problems arising due to a low electrical conductivity is provided granulating the carbon black, after or while adding a water-dispersed silica to the carbon black in a granulator.

TECHNICAL FIELD

The present invention relates to a process for production of a modifiedcarbon black for rubber reinforcement (hereinafter sometimes simplyreferred to as “modified carbon black”). More specifically, the presentinvention relates to a process for production of a modified carbon blackfor rubber reinforcement which has amorphous silica adhered to thesurface thereof. The modified carbon black thus obtained for rubberreinforcement can be formulated into rubber compositions for varioustypes of rubber products such as rubber compositions for tires and alsofor belt conveyors and industrial rolls, to provide superior rubberphysical properties such as abrasion resistance, grip performance, andlow rolling resistance (i.e., low heat buildup) and can be produced,without any major changes in the conventional carbon black productionfacilities, and therefore, can be produced at a low cost.

The present invention also relates to a process for production of arubber composition containing the modified carbon black for rubberreinforcement. More specifically, it relates to a process for productionof a rubber master batch composition containing a diene rubber and amodified carbon black for rubber reinforcement which has awater-dispersed silica adhered to its surface. The rubber compositioncontaining this modified carbon black for rubber reinforcement can beused for various types of rubber products such as tire materials such asthe cap treads and side treads of tires, and also belt conveyors,industrial rubber rolls, and hoses.

BACKGROUND ART

Reinforcing fillers such as carbon black and silica have long been usedfor reinforcing rubber as is well known. In the rubber industry, such asthe tire industry, the practice has been to mix the carbon black usedfor rubber reinforcement with the rubber in advance using the wet carbonblack master batch method so as to simplify mixing step of the carbonblack with the rubber and to improve the dispersion of the carbon blackin the rubber (for example, see Japanese Unexamined Patent Publication(Kokai) No. 59-49247 and Japanese Unexamined Patent Publication (Kokai)No. 63-43937). However, in recent years, the development of superiorsilane coupling agents has led to formulation of silica instead ofcarbon black. Since silica, as compared with carbon black, hasproperties of providing a low tan δ at high temperatures (i.e., around60° C.) and a high tan δ at low temperatures (i.e., around 0° C.), whenused for rubber compositions for tire treads for example, a tire havinga low rolling resistance and a high gripping power can be advantageouslyproduced. However, silica is inferior to carbon black in the abrasionresistance and the low electrical conductivity, and therefore, if usedfor tires, there is the problem that the tire will pick up a charge whendriven on and will cause various problems such as noise and, in somecases, even misoperation in electronic equipments such as radios.

Covering the surface of a pigment, etc. with silica etc. to improve thedispersion and to increase weather resistance has been proposed in, forexample, Japanese Examined Patent Publication (Kokoku) No. 50-14254 andJapanese Examined Patent Publication (Kokoku) No. 7-30269. For example,Japanese Examined Patent Publication (Kokoku) No. 7-30269 discloses amethod of treating the surface of carbon black used for a powder paintcomprising the steps of dispersing carbon black in water, adjusting thepH to 6 or more, and, while maintaining the temperature at least at 70°C., precipitating amorphous silica on the surface of the particles ofcarbon black using sodium silicate. However, none of these publicationsdiscloses the deposition of silica on the surface of the carbon blackused for reinforcing rubber. Further, Japanese Unexamined PatentPublication (Kokai) No. 8-277347 discloses the adhesion of silica to thesurface of carbon black used for rubber reinforcement, but theindustrially efficient production process is not disclosed at all.

When formulating silica into a rubber composition, the silica isdifficult to disperse during the mixing, and therefore, a large amountof labor work is required in the mixing process, and therefore,production of master batches as in the case of carbon black is desired.However, since silica has a coagulating pH (i.e., about 4 to 7)different from the coagulating pH region (i.e., about 2.5 to 3) ofrubber latex and for other reasons, a wet silica master batch has notbeen satisfactorily produced.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a processfor simply and cheaply producing a granulated (beaded) modified carbonblack for reinforcement of rubber having a superior tan δ temperaturedependency of silica and an excellent abrasion resistance andprocessability and further having no problems caused by a low electricalconductivity, without largely changing the existing carbon blackproduction facilities.

Another object of the present invention is to provide a process forproducing a rubber composition containing silica-modified carbon blackfor rubber reinforcement having the superior tan δ temperaturedependency of silica and an excellent abrasion resistance andprocessability and further having no problems caused by a low electricalconductivity and can also be simply and inexpensively produced.

In accordance with the present invention, there is provided a processfor producing a modified carbon black for rubber reinforcementcomprising, in the step of granulating a carbon black when producing themodified carbon black for rubber reinforcement, granulating the carbonblack in a granulator after or while adding water-dispersed silica tothe carbon black.

In accordance with the present invention, there is also provided aprocess for producing a rubber composition comprising:

-   -   mixing (a) 100 parts by weight, in terms of a solid content, of        a diene rubber component and (b) 10 to 250 parts by weight, in        terms of a solid content, of a slurry containing a carbon black        for rubber reinforcement; and    -   coagulating the resultant mixture with a coagulating agent.

In accordance with the present invention, there is further provided aprocess for producing a rubber composition comprising mixing (a) 100parts by weight, in terms of a solid content, of a latex of a dienerubber component and (b′) 10 to 250 parts by weight of a modified carbonblack produced by the above method; and

-   -   coagulating the resultant mixture with a coagulating agent.

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventors engaged in intensive studies on a process forproduction of a modified carbon black for rubber reinforcement having,as mentioned above, a superior tan δ temperature dependency of silica,excellent abrasion resistance, and further having no problems derivedfrom a low electrical conductivity and, as a result, found that it waspossible to produce the desired modified carbon black for rubberreinforcement by adding a water-dispersed silica instead of thegranulating solution (i.e., normally water and a binder) added at thetime of granulating.

As the carbon black for rubber reinforcement used as the startingmaterial for production of a modified carbon black for rubberreinforcement in the present invention, it is possible to use any carbonblack which is generally used in the past for tires and other rubbercompositions. Preferable carbon blacks are the SRF to SAF grades. It ispossible to use the same differently or blend two or more typesdepending on the application of the rubber composition.

A general method for producing a modified carbon black for rubberreinforcement according to the present invention will be explainedbelow. First, as the water-dispersed silica, it is possible to use thoseproduced by mixing and reacting a metal silicate salt and an acid. Theform of the water-dispersed silica (e.g., it may be either a sol or agel) and the concentration of the silica in the water-dispersed silicaare not particularly limited, but a sol type silica in which the silicaparticles exist independently is preferred. A silica concentration of50,000 ppm or less, which is stable for a sol, is suitable. Further, asthe water-dispersed silica, it is also possible to use a commerciallyavailable water-dispersed silica. As a commercially availablewater-dispersed slurry, those having a diameter of the silica particlescontained of from 1 to 100 nm are preferred, more preferably thosehaving a diameter of 5 to 80 nm, and having a sodium ion of 1.0% byweight or less, in terms of Na₂O are preferred. This typewater-dispersed silica is composed of primary particles or aggregatescontaining plural primary particles dispersed in water. Usually, theelectrolyte content is extremely small, and therefore, it is stabilizedin a basic state containing a high concentration of silica. Thus, thewater-dispersed silica may be particularly suitably used when the silicacontent is intended to be increased in modified carbon. In the presentinvention, when producing a modified carbon black, the water-dispersedsilica can be added, without particularly adjusting the pH thereof, butit is also possible, for example to add an acid to adjust the neutralconditions to prevent the gelation of the silica or to prevent thecorrosion of the granulator. Thereafter, the silica is mixed with thecarbon black, whereby the composite of the carbon black is formed.

The characteristic feature of the present invention resides in the factthat the water-dispersed silica is added before or during thegranulating step (either continuous type or batch type) used forproducing a normal or ordinary carbon black to produce a modified carbonblack composed of carbon black having silica is adhered to the surfacethereof.

Normally, water-dispersed silica having a silica concentration of 50,000ppm or less, preferably from 2,500 to 50,000 ppm, is prepared preferablyin an amount of 50 to 1000% by weight of carbon black, depending on theamount of the carbon black supplied, an acid (e.g., sulfuric acid,hydrochloric acid) is added thereto to bring it to the neutral region,then this is added to the carbon black in a granulator.

The carbon black added with the water-dispersed silica in the above waymay be stirred, granulated, and modified at a suitable temperature(e.g., 60° C. to 200° C.) using, for example, a pin type screwgranulator etc. The amount of the water-dispersed silica added to thecarbon black is not particularly limited, but preferably is, in terms ofSiO₂, 0.1 to 50% by weight, more preferably 0.5 to 30% by weight, basedupon the weight of the carbon black.

The rubber composition containing the modified carbon black for rubberreinforcement according to the present invention may be produced, forexample, in the following way. That is, the rubber reinforcement carbonblack and the water-dispersed silica are mixed to make a slurry. Toimprove the dispersibilily of the carbon black, a suitable dispersingagent (e.g., methanol and various surfactants) may also be added. Whenthe pH of this mixture is adjusted to a region where the water-dispersedsilica particles cannot exist independently (e.g., pH of about 7), amodified carbon black having silica adhered to the carbon black isobtained. The slurry thus obtained is mixed with the rubber latex. Notethat the amount of silica adhered to the surface of the carbon black isnot particularly limited, but preferably is 0.1 to 25% by weight, interms of SiO₂, based upon the weight of the silica-modified carbonblack. If the amount of the silica adhered is too large, the coagulationwith the rubber latex tends to become difficult. Further, it is possibleto add the water-dispersed silica to the carbon black, then to granulatethe carbon black in a granulating step and make a slurry by an ordinarymethod, then to mix the resultant modified carbon black with a latex ofthe diene rubber component to obtain a mixture.

The mixture thus obtained of the rubber latex and the modified carbonblack slurry may be used to produce a rubber composition containing themodified carbon black for rubber reinforcement of the present inventionby coagulation by an ordinary method. As the coagulating agent, generalcoagulating agents, for example, an acid such as sulfuric acid andformic acid, an electrolyte such as sodium chloride, a polymercoagulating agent may be used (these may also be used together). Theamount added is the same as in the past, for example, an amount requiredfor adjusting the pH value of the system to 3 to 6.

According to the present invention, the modified carbon black for rubberreinforcement can be formulated into a cross-linkable component such asa diene rubber to obtain a rubber composition superior in abrasionresistance, grip performance, rolling resistance, etc. As such across-linkable rubber, natural rubber (NR), various butadiene rubbers(BR), various styrene-butadiene copolymers (SBR), polyisoprene rubber(IR), butyl rubber (IIR), acrylonitryl-butadiene rubber, chloroprenerubber, ethylene-propylene copolymer rubber, ethylene-propylenedienecopolymer rubber, styrene-isoprene copolymer rubber,styrene-isoprene-butadiene copolymer rubber, isoprene-butadienecopolymer rubber, chlorosulfonated polyethylene, acryl rubber,epichlorohydrin rubber, polysulfide rubber, silicone rubber,fluororubber, urethane rubber, etc. may be exemplified. These may beused alone or in any blend thereof. When a blend is used, the ratio ofthe blend is not particularly limited.

The composition according to the present invention containing themodified carbon black for rubber reinforcement includes, as a solidcontent, 10 to 250 parts by weight of the modified carbon black forrubber reinforcement, more preferably 15 to 200 parts by weight, stillmore preferably 15 to 150 parts by weight, based upon 100 parts byweight of the rubber component. If the amount formulated is too small,when used for various rubber products, since the amount of the modifiedcarbon black for rubber reinforcement normally required (i.e., 10 partsor more) cannot be formulated, sufficient reinforcement is not possibleand, for example, the abrasion resistance etc. deteriorate. Conversely,if too large, there is the danger of the hardness becoming too high, theprocessability falling, or the usefulness as a rubber material otherwisebecoming poorer. It is also possible to use in the rubber compositionany carbon black and/or silica normally formulated into rubbercompositions, in addition to the above water-dispersed silica-modifiedcarbon black.

The rubber composition may also have suitably formulated into it, inaddition to the above rubber, modified carbon black having the silicaadhered to or deposited on its surface, etc., any additives normallyused in the rubber industry such as sulfur, organic peroxides, softeningagents, antioxidants, vulcanization accelerators, fillers, plasticizers,silane coupling agents, etc., if necessary, in an ordinary used amount.

The rubber composition containing the modified carbon black for rubberreinforcement of the present invention may be produced by the samemethod as the ordinary wet carbon black master batch method. A slurry ofcarbon black which has silica adhered to the surface thereof is producedby the above method, then this is mixed with a diene rubber latex (e.g.,SBR latex) in a suitable ratio. Next, a coagulating agent (e.g., apolymer coagulating agent, NaCl, etc.) generally used for the productionof a carbon black master batch, etc. in the past is added forcoagulation. The coagulated rubber composition is separated from theaqueous phase and the moisture is removed by, for example, drying by hotair to obtain the desired rubber master batch composition. Note that itis also possible to add an additive such as an antioxidant process oilor silane coupling agent during the above process if necessary.

The modified carbon black for rubber reinforcement used in the presentinvention is produced as explained above by, for example, causingwater-dispersed silica to adhere to the surface of the carbon black in acarbon black slurry, and therefore, the modified carbon black exists ina slurry state. Accordingly, it is also possible to produce the rubbercomposition of the present invention by mixing this slurry directly withthe rubber latex. This eliminate the labor in the step of mixing thesilica with the rubber and results in good dispersion of the modifiedcarbon black for rubber reinforcement into the rubber. Further, iteliminates the step of recovering and drying the modified carbon blackfor rubber reinforcement from the slurry, and therefore, furthercontributes to the reduction of the production costs.

In a preferred aspect of the present invention, at the time of the abovewet mixing, a process oil such as aromatic oil, paraffinic oil, ornaphthalenic oil and/or a synthetic plasticizer, liquid rubber, or otherliquid generally used in formulating rubber in the past may beformulated into the mixture in an amount of 10 to 200 parts by weightbased upon 100 parts by weight of the diene rubber.

EXAMPLES

The present invention will be explained below in further detail usingExamples, but the invention is of course not restricted to theseExamples in scope.

Examples I-1 to I-6 and Comparative Examples I-1 to I-2

Preparation of Water-Dispersed Silica-Modified Carbon Black

The water-dispersed silica-modified carbon black was produced by thefollowing method.

As the carbon black, two types of HAF (N339) and ISAF (N220) gradesshown in Table I-1 were used. As the water-dispersed silica, apredetermined amount of aqueous JIS No. 1 sodium silicate solution andan amount of dilute sulfuric acid for neutralizing the same were addedto water adjusted to pH 10 with sodium hydroxide so as to finally obtainthree types of sol type water-dispersed silica containing 0.5, 2.5, and5% by weight of SiO₂.

The carbon blacks thus obtained were formed in a reaction furnace,trapped by a bag filter, and transferred to the granulating step.Immediately before the carbon black was introduced into the granulator(i.e., pin type screw granulator), two times the amount of the 0.5, 2.5,or 5% by weight water-dispersed silica as the amount of the carbon blackwas sprayed uniformly over the carbon black as a whole. Next, the carbonblack was conveyed to a granulator (i.e., pin type screw granulator) andgranulated by the usual method to obtain the modified carbon black. Thetemperature of the modified carbon black directly after emerging fromthe granulator (i.e., pin type screw granulator) was about 70 to 80°C.).

Methods for Measurement of Properties of Modified Carbon Black

1) Silica Content

A sample of the modified carbon black was calcified at 600° C. in anelectric furnace, the resultant ash was filtered and washed withdistilled water to remove the salt, then was fluorinated. The decreasein the weight was treated as the silica content. This was shown as apercentage by weight against the original modified carbon.

2) Nitrogen Adsorption Specific Area (N₂SA)

This was measured according to a method of ASTM D3037.

3) Amount of Iodine Absorption

This was measured according to JIS K6221.

Methods for Measurement of Physical Properties of Rubber

Various rubber compositions were prepared by an ordinary method bymixing in a Banbury mixer and rolls according to the followingFormulation Table (i.e., vulcanization conditions: 160° C.×30 minutes)

Formulation Table SBR1502^(*1): 100 parts by weight Reinforcing filler: 50 parts by weight Silane coupling agent^(*2):  3 parts by weight^(*3)Zinc white (JIS No. 3):  3 parts by weight Stearic acid:  2 parts byweight Antioxidant^(*4):  2 parts by weight Powdered sulfur:  2 parts byweight Vulcanization  1 part by weight accelerator^(*5): ^(*1))Nipol1502 (made by Nippon Zeon) ^(*2))Si69 (made by Degussa) ^(*3))Not usedwhen the reinforcing filler is carbon black. ^(*4))Santoflex 13 (made byMonsanto) ^(*5))Santocure NS (made by Monsanto)1) Tensile Strength

This was measured according to a method of JIS K6301.

2) Abrasion Resistance Index

A Lambourn abrasion tester was used for measurement under conditions ofa load of 5 kg, a slip rate of 25%, a time of 4 minutes, and roomtemperature and the loss due to abrasion was indicated as an index. Notethat the larger the figure, the better the abrasion resistance.

3) tan δ

This was measured using a viscoelasticity spectrometer made by ToyoSeiki Seisakusho under an amplitude of ±2%, a frequency of 20 Hz, and astatic stress of 10%.

4) Volume Resistivity

This was measured according to ASTM D991 or JIS K6911.

Compositions were prepared by the types of reinforcing fillers andformulations shown in the formulation table. The results of evaluationof the rubber compositions obtained are shown in Table I-1.

TABLE I-1 Comp. Comp. Ex. I-1 Ex. I-1 Ex. I-2 Ex. I-3 Ex. I-2 Ex.I-4 Ex.I-5 Ex.I-6 Type of carbon N339*¹ N339*¹ N339*¹ N339*¹ N220*² N220*²N220*² N220*² black Silica No Yes Yes Yes No Yes Yes Yes modificationCarbon properties Am't of silica 0 1.0 5.1 10.0 0 0.9 5.3 10.2 (wt %)N₂SA (m²/g) 94 93 101 105 111 115 120 123 Iodine absorption 90 85 74 62117 111 98 90 (mg/g) Rubber physical properties tan δ (0° C.) 0.3030.297 0.297 0.298 0.338 0.335 0.334 0.333 tan δ (60° C.) 0.185 0.1520.155 0.162 0.202 0.182 0.185 0.190 Abrasion 100 103 102 102 100 103 103104 resistance index Volume 1.02 × 1.03 × 1.08 × 1.10 × 1.8 1.8 2.2 2.8resistivity (Ωcm) 10² 10² 10² 10² *¹HAF grade (N339: Seast KH, made byTokai Carbon). *²ISAF grade (N220: DIA BLACK N220, made by MitsubishiChemical).

Examples I-7 to I-30 and Comparative Examples I-3 to I-6

The same procedure was followed as in Examples I-1 to I-6 to preparerubber compositions except for using the commercially availablewater-dispersed silicas a to f shown in Table I-2 for the preparation ofthe modified carbon black for rubber reinforcement. The results ofevaluation obtained according to the Formulation Table of the rubbercompositions shown below are shown in Table I-3.

Formulation Table Natural rubber^(*1):  50 parts by weight Solutionpolymerized SBR^(*2):  50 parts by weight Reinforcing filler:  50 partsby weight Silane coupling agent^(*3): 2.5 parts by weight^(*4) Zincwhite (JIS No. 3):   3 parts by weight Stearic acid:   2 parts by weightAntioxidant^(*5):   3 parts by weight Powdered sulfur:   2 parts byweight Vulcanization accelerator^(*6):   1 part by weight ^(*1))SMR-5L^(*2))NS-116 (made by Nippon Zeon) ^(*3))Si69 (made by Degussa)^(*4))Not used when reinforcing filler is carbon black. ^(*5))Santoflex13 (made by Monsanto) ^(*6))Santocure NS (made by Monsanto)

TABLE I-2 Properties of water-dispersed silica used Silica particleCommercial size (nm) pH SiO₂ (%) Na₂O (%) grade name Manufacturer a 159.8 20.4 0.16 Snowtex 20 Nissan Chemical b 15 8.7 20.3  0.0003 Snowtex CNissan Chemical c 10 9.7 30.4 0.40 Snowtex S Nissan Chemical d 50 10.9 20.3 0.12 Snowtex 20L Nissan Chemical e 76 9.3 40.2   0.00056 Snowtex ZLNissan Chemical f 20 (lenear) 10.3  20.3 0.28 Snowtex UP Nissan Chemical

TABLE I-3 Comp. Comp. Ex. I- Ex. I- Ex.I- Ex.I- Ex.I- Ex.I- Ex.I- Ex.I-3 4 7 8 9 10 11 12 Carbon black N339 N339 N339 N339 N339 N339 N339 N339Water-dispersed silica — — a b c d e f <---added to carbon with no pHadjustment---> N₂SA (m²/g) 94 94 91.08 93.43 85.53 85.61 94.00 83.34Iodine absorption 89 89 72.55 77.74 86.48 86.19 87.28 82.54 (mg/g)Silica content (wt %) 0 0 1 1 1 1 1 1 Si69 formulation 0 2.5 2.5 2.5 2.52.5 2.5 2.5 (phr)*¹ tan δ (0° C.) 0.503 0.514 0.518 0.532 0.533 0.5220.524 0.527 tan δ (60° C.) 0.184 0.177 0.162 0.165 0.169 0.17 0.1620.161 Abrasion resistance 101 102 99 103 99 104 97 108 index Comp. Comp.Ex. I- Ex. I- Ex.I- Ex.I- Ex.I- Ex.I- Ex.I- Ex.I- 3 4 13 14 15 16 17 18Carbon black N339 N339 N339 N339 N339 N339 N339 N339 Water-dispersedsilica — — a b c d e f <---added to carbon after pH 7 adjustment--->N₂SA (m²/g) 94 94 86.59 87.38 88.45 81.65 84.64 86.35 Iodine absorption89 89 78.42 83.55 90.29 85.07 85.78 63.70 (mg/g) Silica content (wt %) 00 1 1 1 1 1 1 Si69 formulation 0 2.5 2.5 2.5 2.5 2.5 2.5 2.5 (phr)*¹ tanδ (0° C.) 0.503 0.514 0.533 0.539 0.528 0.523 0.514 0.524 tan δ (60° C.)0.184 0.177 0.155 0.165 0.169 0.163 0.166 0.161 Abrasion resistance 101102 107 103 97 95 97 107 index Comp. Comp. Ex. I- Ex. I- Ex.I- Ex.I-Ex.I- Ex.I- Ex.I- Ex.I- 5 6 19 20 21 22 23 24 Carbon black N220 N220N220 N220 N220 N220 N220 N220 Water-dispersed silica — — a b c d e f<---added to carbon without pH adjustment---> N₂SA (m²/g) 111 111 103.47104.29 104.48 102.91 114.11 104.61 Iodine absorption 116 116 75.21120.56 109.42 103.47 117.28 115.36 (mg/g) Silica content (wt %) 0 0 1 11 1 1 1 Si69 formulation 0 2.5 2.5 2.5 2.5 2.5 2.5 2.5 (phr)*¹ tan δ (0°C.) 0.533 0.540 0.544 0.548 0.548 0.537 0.547 0.547 tan δ (60° C.) 0.2200.204 0.183 0.185 0.182 0.189 0.188 0.187 Abrasion resistance 103 102103 105 105 102 109 106 index Comp. Comp. Ex. I- Ex. I- Ex.I- Ex.I-Ex.I- Ex.I- Ex.I- Ex.I- 5 6 25 26 27 28 29 30 Carbon black N220 N220N220 N220 N220 N220 N220 N220 Water-dispersed silica — — a b c d e f<---added to carbon after pH 7 adjustment---> N₂SA (m²/g) 111 111 104.17104.63 105.75 102.92 102.20 105.43 Iodine absorption 116 116 114.87110.95 114.65 114.26 116.14 116.61 (mg/g) Silica content (wt %) 0 0 1 11 1 1 1 Si69 formulation 0 2.5 2.5 2.5 2.5 2.5 2.5 2.5 (phr)*¹ tan δ (0°C.) 0.533 0.540 0.540 0.547 0.551 0.540 0.552 0.549 tan δ (60° C.) 0.2200.204 0.185 0.188 0.181 0.186 0.180 0.181 Abrasion resistance 103 102103 110 113 112 109 110 index *¹Parts per 100 parts by weight of rubber.

Note that the modified carbon was produced as follows:

In commercially available water-dispersed silica, a high concentrationof spherical silica particles is stabilized in the relatively high pHalkaline region. For example, those having a concentration of silica ofabout 10 to 50% are generally known. When using these to treat carbonblack, it is necessary to dilute them to a suitable concentration beforeuse in view of the amount of silica to be adhered to the carbon blackand the amount of water required for the granulating solution. Forexample, when using a water-dispersed silica having a silica content of20% by weight to adhere or deposit 1% by weight of silica to or on thecarbon black, it is sufficient to add approximately 0.05 kg of thewater-dispersed silica based upon 1 kg of carbon black. For granulating,however, it is necessary to dilute this by adding the amount of shortageof water since about the same amount of water as the carbon black isnormally required. The concentration of water-dispersed silica thusprepared for granulating may further contain a binder ingredient such asmolasses normally used for granulating carbon black, if necessary.

From the facts that the modified carbon black prepared by the abovemethod does not show any independent spherical silica when observedunder an electron microscope, but shows an amorphous substance nothaving the lamellar-like structure characteristic of carbon black on thesurface of the carbon and that analysis of the ash obtained byincineration shows that a predetermined amount of silica is contained,it is observed that at least a part of the water-dispersed silica formsa composite with the carbon black.

Examples II-1 to II-7 and Comparative Examples II-1 to II-2

Preparation of Modified Carbon Black for Rubber Reinforcement (ExampleII-1)

A mixed slurry was obtained by using 100 g of carbon black for rubberreinforcement (N339) and adding 2 liters of water-dispersed silica. Forthe water-dispersed silica, a predetermined amount of aqueous JIS No. 1sodium silicate solution and an amount of dilute sulfuric acid forneutralizing the same were added to water adjusted to pH 10 by sodiumhydroxide so as to finally obtain a sol type water-dispersed silicacontaining 0.5% by weight of SiO₂.

The water-dispersed silica slurry thus obtained of the carbon blackobtained above was heated to 90° C. and adjusted to pH 7 to obtain thedesired slurry-like substance containing the modified carbon black(i.e., solid content of 5.2% by weight).

Preparation of Modified Carbon Black for Rubber Reinforcement (ExampleII-2 to II-7)

Using a commercially available water-dispersed silica (see Table II-3),modified carbon black for rubber reinforcement was produced in thefollowing way. The commercially available water-dispersed silica shownin Table II-3 was diluted with a suitable amount of water and mixed withungranulated carbon black (N339) in an amount equal to the weight of thecarbon and so that the content of silica in each case became 1% byweight of the total weight of the carbon black and silica, then themixture was granulated by an ordinary carbon black granulator (i.e., pintype screw granulator) at approximately 80° C. This was dried atapproximately 105° C. to obtain the modified carbon black for rubberreinforcement shown in Table II-2.

Preparation of Rubber Composition Containing Modified Carbon Black(Examples II-1 to II-7)

Next, the modified carbon black obtained above was made into a slurry(concentration of 12.5% by weight). 200 g of this and 125 g of SBR 1502latex (concentration of 41% by weight) were mixed, 1000 g of saline(concentration of 3% by weight) was added to this as a coagulatingagent, the mixture was stirred at a temperature of 50° C. for 0.5 hour,then the resultant mixture was dried at 80° C. for 24 hours to obtain arubber composition containing a modified carbon black for rubberreinforcement (i.e., master batches 1 to 7).

Measurement of Silica Content of Modified Carbon Black for RubberReinforcement

A sample of the modified carbon black was calcified at 600° C. in anelectric furnace, then the ash was fluorinated. The reduction in weightwas treated as the silica content adhered. Amounts of silica of 10% byweight and 1% by weight were confirmed as the percentage by weightagainst the original modified carbon.

Various rubber compositions were prepared by an ordinary method bymixing in an internal mixer and rolls according to the followingformulation table (vulcanization conditions: 160° C.×30 minutes). Theresults are shown in Table II-1.

Formulation Table Diene rubber (SBR1502): 100 parts by weight^(*1)Reinforcing filler  50 parts by weight^(*1) (see Table II-1): Silanecoupling agent^(*2):  3 parts by weight^(*3) Zinc white (JIS No. 3):  3parts by weight Stearic acid:  2 parts by weight Antioxidant^(*4):  2parts by weight Powdered sulfur:  2 parts by weight Vulcanizationaccelerator^(*5):  1 part by weight ^(*1))Wet master batch ^(*2))Si69(made by Degussa) ^(*3))Not used when reinforcing filler is carbonblack. ^(*4))Santoflex 13 (made by Monsanto) ^(*5))Santocure NS (made byMonsanto)

TABLE II-1 Ex. II-1 Ex. II-2 Ex. II-3 Ex. II-4 Ex. II-5 Master batchMaster batch 1 Master batch Master Master batch Master batch used 2batch 3 4 5 Type of Modifies carbon Modified Modified Modified Modifiedfiller black 1^(*1) carbon black carbon carbon black carbon black 2^(*1)black 3^(*1) 4^(*1) 5^(*1) Mixing time^(*4) 1 min. 4 min. 1 min. 1 min.1 min. 1 min. Mixing state^(*4) No No No problem No problem No problemNo problem problem problem tan δ 0.162 0.160 0.162 0.163 0.163 0.159(60° C.)^(*5) tan δ (0° C.)^(*5) 0.309 0.312 0.319 0.311 0.313 0.314Abrasion 102 103 108 107 105 103 resistance index^(*6) Ex. 11-6 Ex. 11-7Comp. Ex. II-1 Comp. Ex. II-2 Master batch Master Master batch None (dryblend) None (dry blend) used batch 6 7 Type of Modified Modified Carbonblack^(*2) Silica^(*3) filler carbon carbon black black 6^(*1) 7^(*1)Mixing time^(*4) 1 min. 1 min. 2 min. 4 min 2 min. 4 min. Mixingstate^(*4) No problem No problem Poor No Poor filler No filler problemincorporation problem incorporation tan δ 0.161 0.161 — 0.186 — 0.159(60° C.)^(*5) tan δ (0° C.)^(*5) 0.314 0.320 — 0.305 — 0.310 Abrasion102 104 — 100 — 76 resistance index^(*6) ^(*1)See Table II-2.^(*2)Carbon black N339 (Seast KH, made by Tokai Carbon) ^(*3)Nipsil AQ(made by Nihon Silica) ^(*4)State observed after kneading by 1.5 literBanbury mixer, simultaneously charging rubber and compounding agents(except vulcanization system), then discharging after predeterminedtime. ^(*5)tan δ measured using viscoelasticity spectrometer made byToyo Seiki Seisakusho under conditions of temperature of 0° C. or 60°C., static strain of 10%, dynamic strain of ±2%, and frequency of 20 Hz.^(*6)Measured using Lambourn abrasion tester under conditions of roomtemperature, a slip rate of 35%, and a load of 5 kg. The resultantmixtures were indicated indexed to one of the formulations of carbonblack as 100. The larger the value, the better the abrasion resistanceshown.

TABLE II-2 Rubber Rubber Rubber Rubber Rubber Rubber Rubber reinforc-reinforc- reinforc- reinforc- reinforc- reinforc- reinforc- ing ing inging ing ing ing modified modified modified modified modified modifiedmodified carbon carbon carbon carbon carbon carbon carbon black 1 black2 black 3 black 4 black 5 black 6 black 7 Type of N339 N339 N339 N339N339 N339 N339 carbon black Silica 10% 1% 1% 1% 1% 1% 1% content (%)Type of Made by Commer- Commer- Commer- Commer- Commer- Commer- water-sodium cial cial cial cial cial cial dispersed silicate product productproduct product product product silica and ST-20 ST-C ST-S ST-20L ST-ZLST-UP sulfuric acid Composite Adding to Adding as aqueous solution forgranulating, then granulating. step carbon in slurry state

TABLE II-3 Properties of water-dispersed silica used Silica particleCommercial size (nm) pH SiO₂ (%) Na₂O (%) grade name Manufacturer 15 9.820.4 0.16 Snowtex 20 Nissan Chemical 15 8.7 20.3  0.0003 Snowtex CNissan Chemical 10 9.7 30.4 0.40 Snowtex S Nissan Chemical 50 10.9  20.30.12 Snowtex 20L Nissan Chemical 76 9.3 40.2   0.00056 Snowtex ZL NissanChemical 20 (lenear) 10.3  20.3 0.28 Snowtex UP Nissan Chemical

INDUSTRIAL APPLICABILITY

As is clear from the results of Table I-1 and Table I-2, in the Examplesusing the granulated modified carbon black for rubber reinforcementproduced and granulated by the method according to the presentinvention, a rubber composition is obtained with an excellent abrasionresistance and low electric resistance while being provided with theproperty of silica of a low tan δ at a high temperature (60° C.) and ahigh tan δ at a low temperature (0° C.) compared with the ComparativeExamples, that is, Comparative Examples 1 and 2. That is, according tothe present invention, it is possible to produce a rubber compositioncontaining modified carbon black for rubber reinforcement which, whenused as a tread rubber for a tire, for example, has a high grip, issuperior in fuel economy, is excellent in abrasion resistance, and isfree from the radio noise and adverse influence on electronic equipmentdue to a high electric resistance—by a simpler process and a lower costcompared with the prior art.

As is clear from the results of Table II-1, the process of production ofa rubber composition containing a rubber reinforcing carbon blackmodified with a water-dispersed silica according to the presentinvention enables production by the same method as with and simpler andcheaper than with an ordinary carbon master batch. The compositionobtained also has a lower tan δ at a high temperature (60° C.) and isnot lower in abrasion resistance compared with carbon black.

1. A process for producing a modified carbon black for rubberreinforcement comprising the following steps: (A) (1) adding silica-solto ungranulated carbon black to form a mixture, (2) putting the mixturein a granulator, and (3) granulating the mixture in the granulator, or(B) granulating carbon black in a granulator while adding silica-sol tothe carbon black in the granulator, to produce the modified carbon blackfor rubber reinforcement, wherein the amount of the silica-sol addedbeing 0.1 to 30% by weight, in terms of SiO₂, based upon the weight ofthe carbon black.
 2. A process for producing a modified carbon black asclaimed in claim 1, wherein the silica-sol contains silica particleshaving a diameter of 1 to 100 nm and a sodium ion content of not morethan 1.0% by weight, in terms of Na₂O.
 3. A process for producing amodified carbon black as claimed in claim 1 or 2, wherein the amount ofthe silica-sol added is 0.5 to 30% by weight, in terms of SiO₂, basedupon the weight of carbon black.
 4. A process for producing a modifiedcarbon black as claimed in claim 1 or 2, wherein the amount of thesilica-sol added is 50 to 1000% by weight, based upon the weight of thecarbon black.
 5. A process for producing a modified carbon black asclaimed in claim 1 or 2, wherein an aqueous solution of a binder isfurther added to the silica-sol and the total amount of addition is 50to 1000% by weight, based upon the weight of carbon black.
 6. A processfor producing a modified carbon black for rubber reinforcementcomprising, the following steps: adding silica-sol to ungranulatedcarbon black after the ungranulated carbon black is formed and cooled,and thereafter granulating the carbon black with the added silica-sol ina granulator to produce the modified carbon black for rubberreinforcement, wherein the amount of the Silica-sol added being 0.1 to30% by weight, in terms of SiO₂, based upon the weight of the carbonblack.
 7. A process for producing a modified carbon black for rubberreinforcement comprising granulating carbon black, after the carbonblack is formed and cooled, in a granulator while adding silica-sol tothe carbon black in the granulator to produce the modified carbon blackfor rubber reinforcement, wherein the amount of the silica-sol addedbeing 0.1 to 30% by weight, in terms of SiO₂, based upon the weight ofthe carbon black.